In molding a pattern of a tread portion on a tire, an unvulcanized green tire is pressed against an inner periphery of a tire vulcanizing mold on which ridges corresponding to the surface of the tire tread portion are formed. Thus, a groove pattern of the tire tread portion is molded.
There has been proposed the tire vulcanizing mold having a structure in which the mold is circumferentially segmented into a plurality of pieces, so that it is convenient for releasing a pressurization-molded tire (Patent document 1, for example). In this conventional art, first, a generally cylindrical member (a ring-shaped workpiece) having an inner peripheral shape corresponding to the surface of the tire tread portion is formed, and then cut at several points along the circumference and segmented into a plurality of segmented pieces, with wire electrodischarge machining (or with mechanical wire-cut machining by a wire-cut tool).
Patent document 1: Japanese Patent Application Publication (JP-B) No. 1-29686 (FIG. 1˜FIG. 3)